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An Almost Arthropod: The Onychophoran

Onychoporans share certain characters with arthropods, but are lacking a hard exoskeleton or jointed legs. Onychophorans are probably closely related to arthropods and branched off the tree just before a fully hardened exoskeleton and jointed legs evolved.

Although not officially part of our arthropod story, they certainly deserve a closer look. These candy-colored animals can be bright blue, purple, orange, and green, and are covered in warty bumps. These carnivorous rain-forest dwellers have an unusual hunting style. They pursue small snails, worms, and insects and then shoot a glue-like substance at the intended victim, which quickly hardens and traps the prey.

onychophoran   onychophoran  
A couple of modern onychophorans

Onychophoran reproduction doesn’t necessarily involve much romance. In one South African onychophoran, males stick packets of sperm on the female’s body (apparently anywhere — leg, back, whatever!). Her body senses the sperm packet and dissolves the skin beneath the packet, allowing the sperm to enter her circulatory system and eventually reach her eggs.

First onychophoran photo provided by Dr. Lynn Kimsey and the Bohart Museum of Entomology, University of California Davis; second onychophoran photo provided by M. J. Fouquette at the ASU Tropical Biology website